Buck-boost single-inductor three-output DC-DC converter

Abstract

The invention belongs to the technical field of DC-DC converters, and particularly relates to a buck-boost single-inductor three-output DC-DC converter. The converter comprises a power tube, a divider resistor, a comparator, a control logic module, a turn-on time generation module, a self-adaptive turn-off time module and a current detection module. The power tube is used for a buck-boost topological structure of a traditional DC-DC converter; each path of output voltage of the converter is fed back to the comparator after passing through the divider resistor, and a duty ratio signal of the energy distribution switch is generated in the control logic, so that the power tubes are conducted in sequence; the turn-on time generation module is used for controlling the turn-on time of the system and generating a duty ratio signal of an energy generation switch in control logic, and the turn-on time generation module comprises peak current control and self-adaptive phase control; the steady-state switching frequency of the system is controlled by the self-adaptive turn-off time module; the current detection module detects inductive current information. The method has good key indexes such as cross modulation, response speed, conversion efficiency and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of DC-DC converters, and in particular relates to a buck-boost type single-inductor triple-output DC-DC converter. Background Art

[0002] Although the traditional single-inductor single-output DC-DC converter has a high conversion efficiency, each output requires an off-chip inductor, which greatly wastes PCB area and increases design costs. The single-inductor multiple-output (SIMO) DC-DC converter was proposed to solve this problem.

[0003] The SIMO structure DC-DC converter can generate multiple DC voltage outputs using only one off-chip inductor. While retaining the advantages of high efficiency and strong output current capability of the inductive DC-DC converter, it greatly reduces the number of inductors in the multiple voltage outputs, reduces the volume and cost, and therefore has high academic research and practical application value.

[0004] The single-inductor multi-output DC-DC converter was first patented by Linear Technology in the United States in 1997. The structure adopts the time-multiplexing (TM) control method. The load capacity of the circuit is very limited and has a large output ripple. In recent years, more and more studies have adopted the ordered power distributed control (OPDC) working mode, which effectively improves the load capacity and reduces the output ripple. However, since each output is charged in turn, there is an impact on each other, which leads to a serious intermodulation problem. Therefore, it is necessary to reasonably arrange the distribution of total energy between each output, which increases the design complexity of the control level. In 2010, W.Xu et al. proposed an adaptive feedback matrix to generate common-mode and differential-mode signals of the output voltage, and connected a flying capacitor between the two outputs. This method effectively reduces the impact of intermodulation and reduces the output ripple, but there are still problems such as high complexity and unsuitability for structures with more outputs. In 2014, D.Lv et al. proposed a control method based on ripple adaptive off-time (RBAOT), which uses a comparator for ripple control without the need for a complex compensation network. This greatly simplifies the control stage design and reduces intermodulation. However, this method is only applicable to multi-channel buck outputs and can only work in heavy load mode, so its application is relatively limited.

[0005] For a SIMO DC-DC converter, conversion efficiency, response speed, and intermodulation are three important system indicators. Most of the existing control methods compromise between these three indicators, or sacrifice other indicators in the table to optimize these three indicators. The control method based on RBAOT can take into account key design indicators such as intermodulation, response speed, and conversion efficiency. Therefore, the present invention will continue to use the control method based on RBAOT, and expand it in terms of application scope, and propose a control method suitable for buck-boost SIMO DC-DC converters. Summary of the invention

[0006] The object of the present invention is to provide a buck-boost single inductor three output (SITO) DC-DC converter based on ripple adaptive off-time and phase (RBAOTP) control technology.

[0007] The buck-boost single-inductor three-output DC-DC converter provided by the present invention has a structure as follows: Figure 1 As shown, the structure includes: a power stage 100, a comparator 110, a current detection module 120 (Currnt Sensor), an on-time generating module 130 (on-Time Generator), a control logic module 140 (Control Logic), an adaptive off-time module 150 (Adaptive Off-Time), a power tube driving module 160 (Drive), and a voltage dividing resistor 170; wherein:

[0008] The power stage 100 is used to form a buck-boost topology structure, which consists of six power tubes: Mp1, Mo1 (PMOS), Mo2, Mo3, Mn1, Mn2 (NMOS), an inductor L, three load capacitors C1, C2, C3, and three load resistors RL1, RL2, and RL3. The external input power supply Vg is connected to the source of the power tube Mp1, and the drain of Mp1 is connected to the drain of Mn1 and connected to the left end of the inductor L; the source of the power tube Mn1 is grounded; the drains of the power tubes Mo2, Mo3, and Mn2 are connected to the right end of the inductor L, and the sources are connected to the second output Vout2, the third output Vout3 and the ground respectively. The source of the tube Mo1 is connected to the right side of the inductor L, and the drain is connected to the first output Vout1; the gate of the power tube is controlled by the duty cycle voltage signals of Sp1, So1, So2, So3, Sn1, and Sn2 respectively; the three load capacitors C1, C2, and C3 and the three load resistors RL1, RL2, and RL3 respectively form a parallel structure of capacitors and resistors and are connected to the three outputs Vout1, Vout2, and Vout3; the voltage dividing resistor 170 is used to divide the three outputs Vout1, Vout2, and Vout3 of the converter by two resistors in series and then generate Vfb1, Vfb2, and Vfb3 feedback voltages at the series node;

[0009] The comparator 110 compares the feedback voltages Vfb1, Vfb2, Vfb3 with the reference voltage Vref, and outputs a duty cycle signal to the control logic module 140;

[0010] The current detection module 120 is connected to the left end of the inductor L to obtain the inductor current, outputs the current-to-voltage signal Vsen to control the on-time generation module 130, and outputs the ZCD signal to control the light-load working mode of the control logic module 140;

[0011] The on-time generating module 130 receives the output signal Vsen of the current detecting module 120, the reference voltage Vref, the feedback voltages Vfb1, Vfb2, Vfb3, the power tube gate duty cycle signals Sp1, So1, So2, So3, Sn1, Sn2, and outputs a voltage signal Ton for adjusting the on-time of the system;

[0012] The adaptive off-time module 150 receives the power tube gate duty cycle signals Sp1, So1, So2, So3, Sn1, Sn2 and the clock signal CLK, and outputs a voltage signal Toff to adjust the off-time of the system;

[0013] The control logic module 140 receives the duty cycle signal and the Ton and Toff signals output by the comparator 110 , and outputs the power tube gate duty cycle signals Sp1 , So1 , So2 , So3 , Sn1 , Sn2 through the power tube driving module 160 according to the logic control.

[0014] Different from the existing ripple-based control method, the RBAOTP control method proposed in the present invention introduces adaptive phase control, so that the ripple-based control method can be applied to the buck-boost SIMO DC-DC converter, so that the system can meet more applications, and at the same time designs a light-load working mode to further expand the load range. Specifically:

[0015] (1) About the control logic module

[0016] The power tubes (Mo1, Mo2, Mo3) on the output side of the converter are controlled by the comparator 110 and then turned on in sequence through the control logic module 140. The boost output is powered by the boost mode, and the buck output is powered by the buck mode, completing the charging of the three outputs.

[0017] The charging and discharging timing of the system in steady state and the inductor current waveform are as follows: Figure 2 As shown, at the beginning of each cycle, the power tubes Mp1 and Mn2 are turned on, the power tube Mn1 is turned off, and the inductor L is charged by the input voltage Vg; when the inductor current IL reaches the controlled peak value, the power tube Mn2 is turned off, the power tube Mo1 is turned on, and the boost mode is used to supply power to Vout1; when the feedback voltage Vfb1 obtained by Vout1 after passing through the voltage-dividing resistor 170 reaches the reference voltage Vref, the control logic module 140 controls the power tubes Mn1 and Mo2 to be turned on, Mp1 and Mo1 to be turned off, and Vout2 is supplied with power, and so on until the power supply of Vout3 ends and enters the next cycle.

[0018] (2) About Adaptive Phase Control

[0019] The present invention introduces a charging or freewheeling phase to reduce the influence of intermodulation when the load jumps, and at the same time adjusts the peak current control part to control the peak value of the system inductance current.

[0020] Taking the load jump of the output voltage Vout2 as an example, when the second load changes from light to heavy, a charging phase is added, and the input power supply Vg is connected to power Vout3. While protecting Vout3 from the influence of intermodulation, the inductor L is charged to increase its current to reduce the influence on the system. The charging phase also generates a feedback voltage in the adaptive phase control part in the on-time generation module 130 and feeds it back to the peak current control part in the on-time generation module 130, so that the peak value of the inductor L current increases to meet the energy demand of the load. As the inductor L current increases, the energy distribution time gradually decreases, and finally becomes equal to the off-time generated by the adaptive off-time module 150, and the charging phase is adaptively eliminated;

[0021] When the second load changes from heavy to light, a freewheel phase is added, and the freewheel time is converted into a proportional feedback voltage in the adaptive phase control part in the on-time generating module 130 and fed back to the peak current control part in the on-time generating module 130. The feedback voltage reduces the peak value of the current of the inductor L. As the inductor current decreases, the energy distribution time gradually increases and eventually becomes equal to the off-time generated by the adaptive off-time module, thereby adaptively eliminating the freewheel phase.

[0022] For a load jump situation with the output voltage Vout1 or the output voltage Vout3 , a similar processing method is used.

[0023] (3) About the on-time generation module

[0024] The on-time generation module controls the energy generation process of the system, and is composed of a peak current control part (PCMcontrol) and an adaptive phase control part (Adaptive Phase Control). The structure of the on-time generation circuit is as follows: Figure 5 As shown. The adaptive phase control part inputs the power tube gate duty cycle signal Sp1, So1, So2, So3, Sn1, Sn2, and the charging phase and freewheeling phase are read by the internal logic gate and converted into the control signal Vf in direct proportion. The output control signal Vf is added to the reference voltage Vref to adjust the peak current control part. The peak current control part outputs the Ve voltage signal through the PID compensator by adding the result of the input reference voltage Vref and Vf and the average value Va of the feedback voltages Vfb1, Vfb2, and Vfb3, and outputs the Ton signal after comparison with the output signal Vsen of the current detection module 120 to control the on-time of the system.

[0025] When the system has a freewheeling phase due to changes in external factors such as load, the output voltage Vf of the adaptive phase control part decreases, thereby reducing the peak current of the inductor L to eliminate the freewheeling phase; when the charging phase occurs, the output voltage Vf of the adaptive phase control part increases, thereby increasing the peak current of the inductor L to eliminate the charging phase.

[0026] (4) About adaptive off-time

[0027] Adaptive off-time circuit such as Figure 6As shown, the circuit consists of three parts: a phase frequency detector (PFD), a low-pass filter (CPLPF) with a charge pump structure, and a voltage-controlled delay unit (VCD); the phase frequency detector inputs the power tube gate duty cycle signal Sp1, So1, So2, So3, Sn1, Sn2 and the external clock CLK, and obtains the phase difference between the system shutdown time and the external clock CLK through the internal logic gate structure, and then inputs the low-pass filter (CPLPF). After filtering, the threshold voltage signal Vth is output. After the signal enters the voltage-controlled delay unit (VCD), the Toff signal is output to control the shutdown time of the system. This circuit forms a negative feedback loop similar to a phase-locked loop together with other modules and power stages, and stabilizes the steady-state switching frequency of the system by adjusting the shutdown time.

[0028] The working principle of the circuit is as follows: when the system is in steady-state operation, the output threshold voltage signal Vth of the voltage-controlled delay unit (VCD) remains unchanged. When the system is affected by external factors such as load conditions and input voltage and leaves the steady state, a frequency difference is generated between the system off-time and the external clock CLK. At this time, the adaptive off-time control loop adjusts Vth through negative feedback and then adjusts the off-time, thereby stabilizing the switching frequency.

[0029] In summary, the present invention designs a buck-boost single inductor three output (SITO) DC-DC converter based on ripple adaptive off-time and phase (RBAOTP) control technology, which can adjust the peak value of the inductor L current through adaptive phase control and stabilize the system switching frequency through adaptive off-time. It has good key indicators such as intermodulation, response speed, and conversion efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 FIG. 1 is a schematic diagram of the structure of a buck-boost SITO DC-DC converter according to the present invention.

[0031] Figure 2 It is a diagram of the steady-state charge and discharge timing of the buck-boost SITO DC-DC converter of the present invention.

[0032] Figure 3 This is the principle diagram of adaptive phase control when the load changes from light to heavy.

[0033] Figure 4 This is the principle diagram of adaptive phase control when the load changes from heavy to light.

[0034] Figure 5 This is a diagram showing the circuit structure for generating the on-time.

[0035] Figure 6 Figure 1 is a schematic diagram of the circuit structure for adaptive off-time generation.

[0036] Figure 7 FIG. 1 is a diagram showing the steady-state characteristics of the buck-boost SITO DC-DC converter of the present invention.

[0037] Figure 8 The simulation results after load jump response, where (a) is from heavy load to light load, and (b) is from light load to heavy load.

[0038] Fig. 9 This is the simulation curve of conversion efficiency. DETAILED DESCRIPTION

[0039] The present invention is further described below by way of embodiments in conjunction with the accompanying drawings.

[0040] The present invention designs a buck-boost single-inductor three-output DC-DC converter, wherein the design indicators are shown in Table 1.

[0041] Table 1 Performance indicators of the designed single inductor multiple output converter

[0042] Technology TSMC 0.18μm 1P6M BCD Input voltage 2.7V~4.2V Output voltage 5V, 1.8V, 1V Maximum output power 1.56W Off-chip inductor 3.3μH Output Capacitor 10μF Switching frequency 1MHz Peak conversion efficiency >90％ Output ripple <30mV Load transient response <0.15mV / mA Intermodulation <0.05mV / mA

[0043] The entire buck-boost single inductor triple output DC-DC converter works as follows:

[0044] The power stage 100 forms a topological structure of a buck-boost type single inductor three-output DC-DC converter. The three outputs Vout1, Vout2, and Vout3 generate three feedback voltages Vfb1, Vfb2, and Vfb3 after passing through the voltage divider resistor 170. The feedback input comparison 110 is compared with the reference voltage Vref and then input into the control logic module 140. After passing through the power tube driver 160, the power tubes Mo1, Mo2, and Mo3 are controlled to be disconnected, thereby completing the energy distribution process. At the same time, the current detection module 120 detects the current in the inductor L and then outputs a voltage signal Vsen to control the on-time generation module 130 to generate a Ton signal to adjust the on-time of the system; the adaptive off-time module 150 generates a Toff signal to adjust the off-time of the system to stabilize the switching frequency of the system. The Ton signal and the Toff signal are input into the control logic module 140, and after passing through the power tube driver 160, the power tubes Mp1, Mn1, and Mn2 are controlled to be disconnected, thereby completing the energy generation process. Accordingly, the three outputs Vout1, Vout2, and Vout3 of the converter are completed.

[0045] The post-simulation results of the steady-state characteristics of the system are as follows: Figure 7As shown, the three output voltages are all stable at the set voltage values. The load condition at this time is Iload1=Iload2=Iload3=200mA, the maximum output ripple is 23mV of Vout1, and the steady-state switching frequency is controlled at around 1MHz. During the energy distribution process, the three outputs Vout1, Vout2, and Vout3 are selected in turn.

[0046] When Iload1=180mA, Iload3=100mA, and Iload2 jumps between 50mA and 200mA, the load jump response of the system is as follows: Figure 8 As shown. Figure 8 (a) It can be seen that when the load changes from heavy load to light load, due to the existence of ripple control and freewheeling phase, the system has almost no intermodulation effect. Only due to the change in ripple size, the DC value of Vout1 changes by about 1mV, and the DC value of Vout3 changes by less than 1mV. The overshoot voltage of Vout2 is mainly a switching glitch signal, and its load transient response is 0.067mV / mA. Figure 8 (b) It can be seen that when the load changes from light load to heavy load, the ripple peak of the output voltage remains at the reference voltage, while the valley value decreases, the load transient response generated is 0.11mV / mA, the intermodulation generated is 0.04mV / mA, and the response time is less than 5μs. It can be seen that the ripple-based adaptive off-time and phase control method proposed in the present invention can quickly respond to load changes with small intermodulation.

[0047] When the input voltage Vg = 3.3V, the system conversion efficiency changes with the output power. Fig. 9 As shown, the peak conversion efficiency of the system is 94.5%, which occurs when the output power is about 1.1W. When the three-way load current is 1mA, the conversion efficiency is 81.5%. The static power consumption of the control stage is mainly contributed by circuits such as the comparator, error amplifier, and adaptive off-time module.

Claims

1. A buck-boost type single inductor three-output DC-DC converter, characterized in that: include: A power stage (100), a comparator (110), a current detection module (120), an on-time generation module (130), a control logic module (140), an adaptive off-time module (150), a power tube driving module (160), and a voltage dividing resistor (170); wherein: The power stage (100) is used to form a buck-boost topology structure, and is composed of six power tubes (Mp1, Mo1, Mo2, Mo3, Mn1, Mn2), an inductor (L), three load capacitors (C1, C2, C3), and three load resistors (RL1, RL2, RL3) connected in a circuit. An external input power source Vg is connected to the source of the first power tube (Mp1), the drain of the first power tube (Mp1) is connected to the drain of the fifth power tube (Mn1), and is connected to the left end of the inductor (L); the source of the fifth power tube (Mn1) is grounded; the drains of the third power tube (Mo2), the fourth power tube (Mo3), and the sixth power tube (Mn2) are connected to the right end of the inductor (L), and the sources are connected to the second output (Vout2), the third output (Vout3), and the fourth output (Vout4). out3) and ground, the source of the second power tube (Mo1) is connected to the right side of the inductor (L), and the drain is connected to the first output (Vout1); the gate of the power tube is controlled by six duty cycle voltage signals (Sp1, So1, So2, So3, Sn1, Sn2); three load capacitors (C1, C2, C3) and three load resistors (RL1, RL2, RL3) respectively form a parallel structure of capacitors and resistors and are respectively connected to the three outputs (Vout1, Vout2, Vout3); the voltage dividing resistor (170) is used to divide the three outputs (Vout1, Vout2, Vout3) of the converter by two resistors in series and then generate three feedback voltages (Vfb1, Vfb2, Vfb3) at the series node; The comparator (110) compares the three feedback voltages (Vfb1, Vfb2, Vfb3) with the reference voltage Vref, and outputs a duty cycle signal to the control logic module (140); The current detection module (120) is connected to the left end of the inductor (L) to obtain the inductor current, outputs a current-to-voltage signal (Vsen) to control the on-time generation module (130), and simultaneously outputs a ZCD signal to control the light-load working mode of the control logic module (140); The on-time generating module (130) receives the output signal Vsen of the current detecting module (120), the reference voltage Vref, three feedback voltages (Vfb1, Vfb2, Vfb3), and six power tube gate duty cycle signals (Sp1, So1, So2, So3, Sn1, Sn2), and outputs a voltage signal Ton for adjusting the on-time of the system; An adaptive off-time module (150) receives six power tube gate duty cycle signals (Sp1, So1, So2, So3, Sn1, Sn2) and a clock signal CLK, and outputs a voltage signal Toff to adjust the off-time of the system; The control logic module (140) receives the duty cycle signal, the output voltage signal Ton and the output voltage signal Toff outputted by the comparator 110, and outputs six power tube gate duty cycle signals (Sp1, So1, So2, So3, Sn1, Sn2) through the power tube driving module (160) according to logic control.

2. The buck-boost single-inductor triple-output DC-DC converter according to claim 1, characterized in that: In the control logic module, the second, third and fourth power tubes (Mo1, Mo2 and Mo3) located on the output side of the converter are controlled by the comparator (110) and then by the control logic module (140) to be turned on in sequence, the boost output is powered by the boost mode, and the buck output is powered by the buck mode, so as to complete the charging of the three outputs; The charging and discharging timing sequence in steady state is as follows: at the beginning of each cycle, the first and sixth power tubes (Mp1, Mn2) are turned on, the fifth power tube (Mn1) is turned off, and the inductor (L) is charged by the input voltage Vg; when the inductor current IL reaches the controlled peak value, the sixth power tube (Mn2) is turned off, the second power tube (Mo1) is turned on, and the first output voltage (Vout1) is powered by the boost mode; when the feedback voltage Vfb1 obtained after the first output voltage (Vout1) passes through the voltage divider resistor (170) reaches the reference voltage Vref, the control logic module (140) controls the fifth and third power tubes (Mn1, Mo2) to be turned on through the power tube driver (160), the first and second (Mp1, Mo1) are turned off, and the second output voltage (Vout2) is powered, and so on, until the third output voltage (Vout3) is powered and enters the next cycle.

3. The buck-boost single-inductor triple-output DC-DC converter according to claim 2, characterized in that: Adaptive phase control can be performed, including: when the load jumps, the charging or freewheeling phase is introduced to reduce the impact of intermodulation, and the peak current control part is adjusted to control the system inductor current peak; specifically: For the load jump of the second output voltage (Vout2), when the second load changes from light to heavy, a charging phase is added, and the input power supply Vg is connected to supply power to the third output voltage (Vout3). While protecting the third output voltage (Vout3) from the influence of intermodulation, the inductor (L) is charged to increase its current to reduce the influence on the system. The charging phase also generates a feedback voltage in the adaptive phase control part in the on-time generating module (130) and feeds it back to the peak current control part in the on-time generating module (130), so that the peak value of the inductor (L) current increases to meet the energy demand of the load. As the inductor (L) current increases, the energy distribution time gradually decreases and finally becomes equal to the off-time generated by the adaptive off-time module (150), thereby adaptively eliminating the charging phase. When the second load changes from heavy to light, a freewheeling phase is added, and the freewheeling time is converted into a proportional feedback voltage in the adaptive phase control part in the on-time generation module (130) and fed back to the peak current control part in the on-time generation module (130). The feedback voltage causes the peak value of the inductor (L) current to decrease. As the inductor current decreases, the energy distribution time gradually increases and eventually becomes equal to the off-time generated by the adaptive off-time module (150), thereby adaptively eliminating the freewheeling phase.

4. The buck-boost single-inductor triple-output DC-DC converter according to claim 3, characterized in that: In the on-time generation module, the energy generation process is composed of a peak current control part and an adaptive phase control part; the adaptive phase control part inputs six power tube gate duty cycle signals (Sp1, So1, So2, So3, Sn1, Sn2), reads the charging phase and the freewheeling phase by the internal logic gate, and converts them into a control signal Vf in direct proportion; the output control signal Vf is added to the reference voltage Vref to adjust the peak current control part; the peak current control part outputs the Ve voltage signal through a PID compensator through the result of adding the input reference voltage Vref and the control signal Vf and the average value Va of three feedback voltages (Vfb1, Vfb2, Vfb3), and outputs the Ve voltage signal through a PID compensator internally, and inputs the Ve voltage signal together with the output signal Vsen of the current detection module (120) into a comparator for comparison, and then outputs the Ton signal to control the on-time of the system; When the system has a freewheeling phase due to changes in external factors such as load, the output voltage Vf of the adaptive phase control part decreases, thereby reducing the peak current of the inductor L to eliminate the freewheeling phase; when the charging phase occurs, the output control signal Vf of the adaptive phase control part increases, thereby increasing the peak current of the inductor L to eliminate the charging phase.

5. The buck-boost single-inductor triple-output DC-DC converter according to claim 4, characterized in that: The adaptive off-time circuit (150) is composed of three parts: a phase frequency detector (PFD), a low-pass filter (CPLPF) with a charge pump structure, and a voltage-controlled delay unit (VCD); the phase frequency detector inputs six power tube gate duty cycle signals (Sp1, So1, So2, So3, Sn1, Sn2) and an external clock CLK, obtains the phase difference between the system off-time and the external clock CLK through an internal logic gate structure, and then inputs the low-pass filter (CPLPF), outputs a threshold voltage signal Vth after filtering, and outputs a Toff signal after the signal enters the voltage-controlled delay unit (VCD) to control the off-time of the system; the circuit forms a negative feedback loop similar to a phase-locked loop together with other modules and a power stage, and stabilizes the steady-state switching frequency of the system by adjusting the off-time; The working process of the circuit is as follows: when the system is in steady-state operation, the output threshold voltage signal Vth of the voltage-controlled delay unit (VCD) remains unchanged. When the system is out of steady state due to external factors such as load conditions and input voltage, a frequency difference is generated between the system off-time and the external clock CLK. At this time, the adaptive off-time control loop adjusts Vth through negative feedback and then adjusts the off-time, thereby stabilizing the switching frequency.

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